The present invention relates to bookbinding and like machines in general, and more particularly to improvements in apparatus for gathering folded sheets on a moving conveyor so that the conveyor accumulates groups each containing two or more superimposed opened sheets which ride on the conveyor on their way to a stapling or other processing station.
Apparatus of the type to which the present invention pertains are disclosed in the commonly owned Swiss patent application Ser. No. 9140/80-0 as well as in numerous U.S. and foreign patents of the assignee. Reference may be had, for example, to U.S. Pat. Nos. 4,085,927, 4,491,311 and 4,401,299 whose disclosures are incorporated herein by reference.
A drawback of presently known apparatus for gathering folded sheets is that they cannot predictably manipulate so-called square folded sheets wherein two closed or folded and several unfolded or non-folded edges extend transversely of the folded back. The reason is that, when a freshly opened square folded sheet is allowed to descend toward, or is propelled onto, the conveyor which gathers the deposited sheet with one or more additional sheets to advance the thus obtained group to the stapling station or to another processing station, the unfolded edges of the descending square folded sheet continue to open up under the action of air and interfere with predictable deposition of the sheet on the conveyor, especially if the transfer of such sheets from a magazine to the conveyor must take place at frequent intervals, i.e., when successive opened sheets travel at a high speed between the so-called spreading or opening conveyors and the upper reach of a customary chain conveyor for opened sheets.
Attempts to overcome the just discussed problems which arise in connection with the gathering of square folded sheets include such positioning of stops which are adjacent to the path of movement of successive sheets immediately upon extraction from the magazine that the folded backs of the freshly extracted sheets are inclined with reference to the path of movement of opened sheets on the upper reach of the chain conveyor. The arrangement is such that the folded edges of the opened sheets are located ahead of the unfolded edges, as considered in the direction of travel of the upper reach of the chain conveyor, and that the opening or spreading conveyors positively entrain and guide the folded edges to a level below the upper reach so as to ensure that the fluttering unfolded (trailing) edges cannot interfere with predictable deposition of the sheets. This proposal exhibits the serious drawback that each freshly extracted sheet must change its orientation with reference to the withdrawing drum (in order to change the orientation of the folded back relative to the path of movement of the upper reach of the chain conveyor). Such change of orientation entails deformation of and/or other damage to the sheets, especially when the sheets must be transferred at a high frequency in a modern gathering apparatus. Moreover, a deformed or otherwise damaged sheet cannot be deposited on the chain conveyor with a required degree of predictability so that the shifting of sheets with reference to the withdrawing drum is to no avail.